Control channel for wireless communication

ABSTRACT

A scheme for transmission of control channel information in a compact form intended to support SPS (Semi-Persistent Scheduling) in a wireless communication system. As applied to LTE, the scheme is to indicate a pre-configured UE-specific resource allocation in a Downlink Control Information (DCI) format containing information for multiple UEs in the same PDCCH. In order to avoid increasing the number of blind decodes, the DCI format size may be the same as an existing DCI format. Preferably the size of the new format is the same as that of DCI formats 0/1A/3/3A. The number of required bits per UE is minimised by signalling only one of a limited set of DCI messages per UE. The scheme provides a means for re-configuring SPS resources for multiple UEs using a single PDCCH transmission, whilst enabling better support for variable packet sizes and variable intervals between packets than currently defined SPS.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of international Application No.PCT/EP2011/069444, filed Nov. 4, 2011, which claims priority frominternational Application No. PCT/EP2011/063164, filed Jul. 29, 2011,now pending, the contents of which are herein wholly incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to wireless communication systems, forexample systems based on the 3GPP Long Term Evolution (LTE) and 3GPPLTE-A groups of standards.

BACKGROUND OF THE INVENTION

Wireless communication systems are widely known in which base stations(BSs) form “cells” and communicate with user equipments (UEs) (alsocalled subscriber or mobile stations) within range of the BSs.

In such a system, each BS divides its available bandwidth, i.e.frequency and time resources in a given cell, into individual resourceallocations for the user equipments which it serves. The user equipmentsare generally mobile and therefore may move among the cells, prompting aneed for handovers of radio communication links between the basestations of adjacent cells. A user equipment may be in range of (i.e.able to detect signals from) several cells at the same time, but in thesimplest case it communicates with one “serving” or “primary” cell.

Modern wireless communication systems such as LTE and LTE-A are hugelycomplex and a full description of their operation is beyond the scope ofthis specification.

However, for assisting understanding of the inventive concepts to bedescribed later, some outline will be given of some of the features ofLTE which are of particular relevance in the present invention.

Basic LTE Network Topology

The network topology in LTE is illustrated in FIG. 1. As can be seen,each UE 12 connects over a wireless link via a Uu interface to an eNB11, and the network of eNBs is referred to as the eUTRAN 10.

Each eNB 11 in turn is connected by a (usually) wired link using aninterface called S1 to higher-level or “core network” entities,including a Serving Gateway (S-GW 22), and a Mobility Management Entity(MME 21) for managing the system and sending control signalling to othernodes, particularly eNBs, in the network. In addition, a PDN or PacketData Network Gateway (P-GW) is present, separately or combined with theS-GW 22, to exchange data packets with any packet data network includingthe Internet. The core network 20 is called the EPC or Evolved PacketCore.

Machine Type Communication (MTC) and Machine-to-Machine (M2M)Communication

Machine-to-Machine (M2M) communication, usually referred to in thecontext of LTE as Machine Type Communication (MTC), is a form of datacommunication which involves one or more entities that do notnecessarily need human interaction; in other words the ‘users’ may bemachines.

MTC is different from current communication models as it potentiallyinvolves very large number of communicating entities (MTC devices) withlittle traffic per device. Examples of such applications include: fleetmanagement, smart metering, product tracking, home automation, e-health,etc.

MTC has great potential for being carried on wireless communicationsystems (also referred to here as mobile networks), owing to theirubiquitous coverage. However, for mobile networks to be competitive formass machine-type applications, it is important to optimise theirsupport for MTC. Current mobile networks are optimally designed forHuman-to-Human communications, but are less optimal formachine-to-machine, machine-to-human, or human-to-machine applications.It is also important to enable network operators to offer MTC servicesat a low cost level, to match the expectations of mass-marketmachine-type services and applications.

To fully support these service requirements, it is necessary to improvethe ability of mobile networks to handle machine-type communications.

In the LTE network illustrated in FIG. 2, a group of MTC devices 200 isserved by an eNB 11 which also maintains connections with normal UEs 12.The eNB receives signalling from the MME 21 and data (for example, arequest for a status report from a supervisor of the MTC devices) viathe S-GW 22.

Thus, there is a MTCu interface analogous to the Uu interface, and theMTC devices will be served in a similar way to normal user equipments bythe mobile networks. When a large number of MTC devices connect to thesame cell of a UMTS RNS or an LTE eNB, each of the devices will needresources to be allocated to support the individual devices'applications even though each MTC device may have little data.

In the remainder of this specification, the term “UE” includes “MTCdevice” unless otherwise demanded by the context.

For assisting understanding of the inventive concepts to be describedlater, some outline will be given of some specific aspects or featuresof LTE which are of particular relevance in the present invention.

OFDMA and SC-FDMA

In the downlink of an LTE system, in other words the direction oftransmission from the base station (eNB) towards the user equipments(UEs), individual OFDM subcarriers or sets of subcarriers are assignedto different user equipments. The result is a multi-access systemreferred to as OFDMA (Orthogonal Frequency Division Multiple Access). Byassigning distinct frequency/time resources to each user equipment in acell, OFDMA can substantially avoid interference among the users servedwithin a given cell.

The UEs are allocated a specific number of subcarriers for apredetermined amount of time. An amount of resource consisting of a setnumber of subcarriers and OFDM symbols is referred to as a resourceblock (RB) in LTE. RBs thus have both a time and frequency dimension.Allocation of RBs is handled by a scheduling function at the eNB.

The uplink in an LTE wireless communication system employs a variant ofOFDMA called Single-Carrier FDMA (SC-FDMA). Essentially, SC-FDMA is alinearly precoded OFDMA scheme, involving an additional DFT step beforethe conventional OFDMA processing. Access to the uplink by multiple UEsis enabled by assigning to each UE a distinct set of non-overlappingsub-carriers. This allows a single-carrier transmit signal, reducing thepeak-to-average power ratio (PAPR) in comparison with OFDMA.

Frame Structure and Resource Blocks

In a wireless communication system such as LTE, data for transmission onthe downlink is organised in OFDMA frames each divided into a number ofsub-frames. Various frame types are possible and differ betweenfrequency division duplex (FDD) and time division duplex (TDD) forexample.

FIG. 3 shows a generic frame structure for LTE, applicable to thedownlink, in which the 10 ms frame is divided into 20 equally sizedslots of 0.5 ms. A sub-frame SF consists of two consecutive slots, soone radio frame contains 10 sub-frames.

The transmitted signal in each slot is described by a resource grid ofsub-carriers and available OFDM symbols, as shown in FIG. 4. Eachelement in the resource grid is called a resource element (RE) and eachresource element corresponds to one symbol.

For each transmission time interval of 1 ms, a new scheduling decisionis taken regarding which UEs are assigned to which time/frequencyresources during this transmission time interval, the scheduling beingmade in units of resource blocks (RB). As shown in FIG. 4, one resourceblock is usually defined as 7 consecutive OFDM symbols in the timedomain and 12 consecutive sub-carriers in the frequency domain. Severalresource blocks may be allocated to the same UE, and these resourceblocks do not have to be contiguous with each other. Schedulingdecisions are taken at the eNB, using a scheduling algorithm which takesinto account the radio link quality situation of different UEs, theoverall interference situation, Quality of Service requirements, servicepriorities, etc.

Channels

In LTE, several channels for data and control signalling are defined atvarious levels of abstraction within the system. FIG. 5 shows some ofthe channels defined in LTE at each of a logical level, transport layerlevel and physical layer level, and the mappings between them. Forpresent purposes, the channels at the physical layer level are of mostinterest.

On the downlink, user data is carried on the Physical Downlink SharedChannel (PDSCH). There are various control channels on the downlink,which carry signalling for various purposes including so-called RadioResource Control (RRC), a protocol used as part of radio resourcemanagement, RRM. In particular this signalling comprises the PhysicalDownlink Control Channel, PDCCH (see below).

Meanwhile, on the uplink, user data and also some signalling data iscarried on the Physical Uplink Shared Channel (PUSCH). By means offrequency hopping on PUSCH, frequency diversity effects can be exploitedand interference averaged out. The control channels include a PhysicalUplink Control Channel, PUCCH, used to carry signalling from UEsincluding channel state information (CSI), as represented for example bychannel quality indication (CQI) reports, and scheduling requests.

PDCCH and DCI

In LTE, both the DL and UL are fully scheduled since the DL and ULtraffic channels are dynamically shared channels. This means that PDCCHmust provide scheduling information to indicate which users shoulddecode the physical DL shared channel (PDSCH) in each sub-frame andwhich users are allowed to transmit on the physical UL shared channel(PUSCH) in each sub-frame. PDCCH is used to carry schedulinginformation—called downlink control information, DCI—from base stations(called eNBs in LTE) to individual UEs. Conventionally, one PDCCHmessage contains one DCI format. This is often intended for oneindividual UE, but some messages are also broadcast (e.g. intended formultiple UEs within a cell). Thus PDCCH can also contain informationintended for a group of UEs, such as Transmit Power Control (TPC)commands. In addition the PDCCH can be used to configure asemi-persistent schedule (SPS), where the same resources are availableon a periodic basis. The motivation for SPS is to support applications.

PDCCH is transmitted on an aggregation of one or several consecutivecontrol channel elements (CCEs), where a control channel elementcorresponds to 9 resource element groups (REG). Each REG in turnoccupies four of the Resource Elements (REs) shown in FIG. 4.

More particularly PDCCH contains:

-   -   the resource allocations for the downlink transport channel        DL-SCH    -   Transmit Power Control (TPC) commands for PUCCH and the uplink        transport channel UL-SCH; these commands enable the UE to adjust        its transmit power to save battery usage    -   Hybrid-Automatic Repeat Request (HARQ) setup information    -   MIMO (see below) precoding information.

A cyclic redundancy check (CRC) is used for error detection of the DCI.The entire PDCCH payload is used to calculate a set of CRC parity bits,which are then appended to the end of the PDCCH payload.

As multiple PDCCHs relevant to different UEs can be present in onesub-frame, the CRC is also used to specify which UE a PDCCH is relevantto. This is done by scrambling the CRC parity bits with a Radio NetworkTemporary Identifier (RNTI) of the UE. Various kinds or RNTI aredefined, as explained in more detail below.

The size of the DCI depends on a number of factors, and thus it isnecessary that the UE is aware of the size of the DCI, either by RRCconfiguration or by another means to signal the number of symbolsoccupied by PDCCH.

Depending on the purpose of the DCI message, different DCI formats aredefined. The DCI formats include:

-   -   Format 0 for transmission of uplink shared channel (UL-SCH)        allocation    -   Format 1 for transmission of DL-SCH allocation for Single Input        Multiple Output (SIMO) operation    -   Format 1A for compact transmission of DL-SCH allocation for SIMO        operation or allocating a dedicated preamble signature to a UE        for random access    -   Format 3 and format 3A for transmission of TPC command for an        uplink channel.

DCI Formats 3 and 3A carry multiple power control bits representingmultiple power control commands, each power control command beingintended for a different UE. The main application of interest forFormats 3 and 3A is to support SPS in the uplink (since UE specificPDCCH DCI formats to carry power control commands are not thenrequired).

Further details of the full set of DCI formats already defined in LTEcan be found In the document 3GPP TS36.212 “Evolved UniversalTerrestrial Radio Access (E-UTRA): Multiplexing and channel coding”,hereby incorporated by reference. As an example, format 0 is specifiedas follows:

DCI Format fields size description ‘Format0’ DCIFormat — ‘Format0’:indicates the DCI format to the UE AllocationType 1-bit Resourceallocation header: type0, type1 (for uplink frequency hopping)Allocation variable Resource block assignment/allocation: indicates thestarting RB as well as the number of contiguous RBs allocated to the UEHoppingFlag 1-bit PUSCH hopping flag (for uplink frequency hopping)ModCoding 5-bits Modulation, coding scheme and redundancy versionNewData 1-bit New data indicator (a new transmission is to be sent) TPC2-bits PUSCH TPC command for adapting the UE's transmit power CShiftDMRS3-bits Cyclic shift for an uplink demodulation reference signal DM RSCQIReq 1-bit CQI request: requests UE to send a channel qualityindication DAI 2-bits Downlink assignment index (TDD only) ULIndex2-bits UL index (TDD only)

Since, as already mentioned, multiple UEs can be scheduled within thesame sub-frame, conventionally therefore multiple DCI messages are sentusing multiple PDCCHs.

The format to be used depends on the purpose of the control message. Forexample, DCI format 1 is used for the assignment of a downlink sharedchannel resource when no spatial multiplexing is used (i.e. thescheduling information is provided for one code word transmitted usingone spatial layer only). The information provided enables the UE toidentify the resources, where to receive the PDSCH in that sub-frame,and how to decode it. Besides the resource block assignment, this alsoincludes information on the modulation and coding scheme and on thehybrid ARQ protocol used to manage retransmission of non-received data.

A UE needs to check all possible combinations of PDCCH locations, PDCCHformats, and DCI formats and act on those message with correct CRCs(taking into account that the CRC is scrambled with a RNTI). To reducethe required amount of ‘blind decoding’ of all the possiblecombinations, for each UE a limited set of CCE locations is definedwhere a PDCCH may be placed. The set of CCE locations in which the UEmay find its PDCCH is called the “search space”. In LTE, separateUE-specific and common search spaces are defined, where a dedicatedsearch space is configured for each UE individually, while all UEs areinformed of the extent of the common search space.

RNTIs

RNTIs or Radio Network Temporary Identifiers, mentioned earlier, areused by the eNB to scramble the CRC applied to the PDCCH payload. Typesof RNTI currently defined in LTE include the following.

P-RNTI (Paging RNTI):

To receive paging messages from E-UTRAN, UEs in an idle mode monitor thePDCCH channel for a P-RNTI value used to indicate paging. If theterminal detects a group identity used for paging (the P-RNTI) when itwakes up, it will process the corresponding downlink paging messagetransmitted on the PCH.

SI-RNTI (System Information RNTI):

The presence of system information on DL-SCH in a sub-frame is indicatedby the transmission of a corresponding PDCCH marked with a specialSystem Information RNTI (SI-RNTI). This PDCCH message indicates thetransport format and physical resources (set of resource blocks)allocated for system-information transmission.

M-RNTI (MBMS RNTI):

This is used in Multimedia Broadcast Multicast Services (MBMS), apoint-to-multipoint transmission scheme available in LTE.

RA-RNTI (Random Access RNTI):

The RA-RNTI is used on the PDCCH when Random Access Response (RAR)messages are transmitted, to identify which time-frequency resource wasutilized by the UE to transmit a Random Access preamble. In the event ofa collision when multiple UEs select the same signature in the samepreamble time-frequency resource, they each receive the RAR message.

C-RNTI (Cell RNTI):

The C-RNTI is used by a given UE while it is in a particular cell, afterit has successfully joined the network by performing a network entryprocess with the eNB of that cell. The C-RNTI is used for normalscheduling of downlink resources for the UE, also called dynamicscheduling as opposed to semi-persistent scheduling (see below).

TC-RNTI:

If a UE does not have an allocated C-RNTI, then a Temporary C-RNTI(TC-RNTI) is used for further communication between the terminal and thenetwork. Once the UE has completed the network entry process, theTC-RNTI is changed to a C-RNTI.

SPS-C-RNTI (Semi-Persistent Scheduling C-RNTI):

This form of RNTI is used in SPS (see below). For the configuration orreconfiguration of a persistent schedule, RRC signalling indicates theresource allocation interval at which the radio resources areperiodically assigned to a specific UE. Specific transmission resourceallocations in the frequency domain, and transmission attributes such asthe modulation and coding scheme, are signalled using the PDCCH. Theactual transmission timing of the PDCCH messages is used as thereference timing to which the resource allocation interval applies. Whenthe PDCCH is used to configure or reconfigure a persistent schedule, itis necessary to distinguish the scheduling messages which apply to apersistent schedule from those used for dynamic scheduling. For thispurpose, a special identity is used, known as the Semi-PersistentScheduling C-RNTI (SPS-C-RNTI), which for each UE is different from theC-RNTI used for dynamic scheduling messages.

TPC-PUCCH-RNTI (Transmit Power Control-Physical Uplink ControlChannel-RNTI) and TPC-PUSCH-RNTI (Transmit Power Control-Physical UplinkShared Channel-RNTI):

The power-control message is directed to a group of terminals using anRNTI specific for that group. Each terminal can be allocated twopower-control RNTIs, one for PUCCH power control and the other for PUSCHpower control. Although the power control RNTIs are common to a group ofterminals, each terminal is informed through RRC signaling which bit(s)in the DCI message it should follow.

Further details of RNTIs available in LTE are given by the document 3GPPTS 36.213: “Evolved Universal Terrestrial Radio Access (E-UTRA);Physical layer procedures”, hereby incorporated by reference.

SPS

Semi-Persistent Scheduling, SPS, schedules resources for UEs on anongoing basis and thereby reduces control channel overhead forapplications that require persistent radio resource allocations such asVoIP (Voice over Internet Protocol). In LTE, both the DL and UL arefully scheduled as already mentioned so that without SPS, every DL or ULphysical resource block (PRB) allocation must be granted via a PDCCHmessage. Note that although retransmissions on PUSCH can be madeautonomously without an explicit UL grant, the first transmission wouldrequire a grant. This works well with large packet sizes and only a fewusers to be scheduled each sub-frame. However, for applications thatrequire persistent allocations of small packets, the control channeloverhead due to scheduling information can be greatly reduced with SPS.In SPS, the eNB defines a persistent resource allocation that a usershould expect on the DL or can transmit on the UL. This can also behighly beneficial for MTC for example, where the MTC devices may beexpected to transmit a small amount of data at fixed intervals.

On the other hand, SPS as currently defined has various limitations aswill be explained later.

R-PDCCH

FIGS. 1 and 2 show network topologies in which UEs and/or MTC devicescommunicate directly with a eNB. However, it is likely that practicalLTE deployments will employ relay nodes (RNs) intermediate between UEsor MTC devices and the eNB providing the cell.

A new physical control channel, called the relay physical downlinkcontrol channel (R-PDCCH), may be used to dynamically orsemi-persistently assign resources, within the semi-statically assignedsub-frames, for the relay physical downlink shared channel (R-PDSCH).The R-PDCCH is also used to dynamically or semi-persistently assignresources for the relay physical uplink shared channel (R-PUSCH).

R-PDCCH may be transmitted on a subset (including up to all of) of theOFDM symbols of the sub-frames assigned for the backhaul link (PDSCH).It is transmitted starting from an OFDM symbol within the sub-frame thatis late enough so that the RN can receive it. R-PDCCH may be used toassign DL resources in the same sub-frame and/or in one or more latersub-frames; it may be also be used to assign UL resources in one or morelater sub-frames.

Further details of R-PDCCH can be found in the LTE standards document3GPP TS 36.216: “Evolved Universal Terrestrial Radio Access (E-UTRA);Physical layer for relay operation”, hereby incorporated by reference.In the remainder of this specification, references to PDCCH are to beunderstood as including R-PDCCH unless the context demands otherwise.

DRX and DTX

Discontinuous Reception (DRX) and Discontinuous Transmission (DTX) aretechniques for saving power at the UE, and are also highly relevant toMTC. Both DRX and DTX involve reducing switching off the UE'stransceiver periodically. Although the data throughput capacity isreduced in proportion to power saving, this is often not a problem forMTC devices having only a limited data capacity.

The eNB sets a cycle where the UE is operational for a certain period oftime, during which all the scheduling and paging information istransmitted. Except in DRX mode, the UE's transceiver must be active tomonitor PDCCH (to identify DL data).

Limitations of PDCCH and SPS

Currently in LTE, control channel messages (using PDCCH) may betransmitted to a UE from one or more serving cells. This control channelis typically used to indicate to the UE information about a downlinktransmission that will occur on a downlink data channel (PDSCH) or togrant resources for transmission on an uplink data transmission (onPUSCH). In addition the PDCCH can be used to configure a semi-persistentschedule (SPS), where the same resources are available on a periodicbasis. PDCCH can also contain information intended for a group of UEs.In particular Formats 3 and 3A carry multiple TPC bits, each intendedfor a particular UE. In general however, and particularly for schedulingother than SPS, a separate PDCCH is required for each UE.

A PDCCH transmission typically contains a payload of around 50 bits(including CRC), with additional channel coding to improve robustness totransmission errors. For some applications only small data packets arerequired, so the PDCCH payload may represent a significant overhead.This may be even more significant for some configurations of TDD, with alimited proportion of subframes allocated for DL transmission. Inaddition, there is a limit on the maximum number of PDCCH messages thatcan be transmitted at the same time (i.e. within the same subframe),which may be insufficient to support a large number of active UEstransmitting or receiving only small data packets.

One scenario where such control channel limitations may be significantis for Machine-To-Machine (M2M) Communication or Machine TypeCommunication (MTC). As a particular example, a sensor application mayrequire small data packets (e.g. temperature readings) to be sent atshort intervals from a large number of devices within one cell.

Meanwhile, semi-persistent scheduling (SPS) allows the resourceallocation to be pre-configured. However, changing the resourceallocation (including timing) of SPS for one UE requires a PDCCH messagespecifically for that UE.

In any case the current control channel arrangements intended for SPSsuffer from a number of limitations, some of which are considered here:—

-   -   The availability of resources for SPS is limited to particular        limited set of periodicities    -   The number of resource elements (REs) for SPS is fixed    -   The data rate (transport block size) for SPS is fixed    -   The modulation and coding scheme for SPS is fixed

Scenarios where such control channel limitations may be significant, sothat neither UE-specific PDCCH DCI formats or SPS are directly suitable,could include the following:—

-   -   Applications requiring regular transmission of small packets but        with variable size (e.g. VoIP, where the packets may have one of        a small set of sizes)    -   Applications requiring intermittent or irregular transmission of        small packets of the same size (e.g. a sensor application        sending a reading when the temperature changes)    -   Applications requiring regular transmission of small packets        with the same size (e.g. VoIP) but where the variations in the        radio channel mean that efficient channel adaptation requires        variation of the transmission rate and/or location of the        resource allocation in the frequency domain    -   Applications which could otherwise be supported by SPS but where        the desired HARQ operating point leads to a high probability of        retransmission, each retransmission requiring a PDCCH message.

Therefore means for provision of efficient control channel functionalitywith low overhead for the above, for example by extending SPSfunctionality, is of significant interest.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda wireless communication method in which a base station transmits acontrol signal, the control signal arranged in accordance with apredefined format having a predetermined size in bits and comprising oneor more sets of bits each containing one or more bits;

-   -   wherein a first set of bits within the format is intended for a        first terminal and a set of bits within the format is intended        for a second terminal; and    -   wherein the timing of subsequent transmission and/or reception        by the first terminal is determined by the control signal.

Here, “timing” may refer either to an absolute time for the subsequenttransmission/reception or to a relative time, in other words a timingoffset. Time may be expressed in various ways, for example in units ofsubframes defined in a network to which the base station belongs. Theterm “timing” is thus to be construed broadly. Such a timing offset maybe configured separately for each terminal. The offset may be withrespect to the current subframe, being the subframe in which the controlsignal is received by the terminal.

In the above wireless communication method, the timing of subsequenttransmission and/or reception by the first terminal may depend on thetiming of reception of the control signal.

Alternatively, or in addition, the timing of subsequent transmissionand/or reception by the first terminal depends on the value(s) of thefirst set of bits. For example, the value(s) may represent a number ofsubframes as a timing offset from the current subframe.

The first and second terminals may be regarded as constituting a groupof terminals addressed by the control signal. There may be any number ofother terminals in the group. The terminals may be addressed eithercollectively or individually, or a set of bits may be used to addressthe terminals in common, with other sets of bits intended for eachspecific terminal individually.

Thus, in one embodiment, a second set of bits, distinct from the firstset of bits is intended for the second terminal. In another embodiment,the first set of bits is also intended for the second terminal. Theseembodiments may be combined. That is, in SPS for example, it may bedesirable to set certain parameter values in common for a group ofterminals whilst setting other parameter values individually on aper-terminal basis. This can be achieved by providing one (or more) setof bits for representing common parameter values and other sets of bitsfor configuring terminals individually.

A further possibility is that more than one set of bits is specificallyintended for the same terminal. For example one set of bits may relateto scheduling the terminal on the uplink, and another set of bits toscheduling the same terminal on the downlink.

Preferably, the sets of bits include sets of bits representing values ofone or more parameters, used to control some aspect of operation of theterminals.

Within the control signal, distinct sets of bits may represent the sameparameter(s), allowing different terminals to be configured withdifferent values for those parameters.

A particularly compact form of conveying information within the controlsignal is to use each set of bits to represent one of a plurality ofpredefined sets of parameter values. Thus, the sets of bits may includesets of bits representing a selection among predetermined sets ofparameter values. In this way, a small number of bits can be used to setvalues of a number of different parameters simultaneously. Whilstlacking the flexibility of setting parameter values individually, thisapproach allows UEs to be quickly and efficiently configured withparameter values likely to be broadly suited to the channel conditionsbetween the UE and base station.

The parameter values, or the predetermined sets of parameter values,preferably include parameter values for scheduling transmission and/orreception of the first and second terminals. However, the control signalmay include parameter values for other purposes too, such as powercontrol and/or ACK/NACK, where transmission of “NACK” may alsoimplicitly lead to retransmission of a packet in the uplink.

In a preferred embodiment of the method, transmission and/or receptionby the first terminal occurs in units of subframes and the first set ofbits includes at least one bit indicating any one of:

-   -   whether transmission and/or reception is to be performed in the        current subframe either on a downlink and/or on an uplink;    -   whether transmission and/or reception is to be performed in        subsequent subframes either on a downlink and/or on an uplink;    -   whether transmission and/or reception is to be performed in a        defined subframe which is a defined number of subframes from the        current subframe;    -   whether semi-persistent scheduling, SPS operation is to be        activated or deactivated;    -   a selection among predetermined sets of parameter values for        scheduling; and    -   a selection among a predetermined set of carrier frequencies for        scheduling.

In the above, “scheduling” may refer to semi-persistent scheduling, SPS(or an enhanced version thereof), but is not necessarily limited to SPS.References in this specification to SPS include enhanced semi-persistentscheduling with greater operational flexibility as permitted by thepresent invention, in addition to conventional SPS as already providedfor in the standards.

Currently in LTE, a single control channel (PDCCH) is transmitted to theUE for any UL or DL resource allocation, except for SPS, where theresource allocation is pre-configured. However, changing the resourceallocation (including timing) of SPS for one UE requires a PDCCHmessage. The invention provides a means for re-configuring orre-allocating SPS resources for multiple UEs using a single PDCCHtransmission.

A particular form of the invention is for use in an LTE-based wirelesscommunication system in which the control signals are downlink controlinformation, DCI, and the predefined format is a DCI format transmittedon a physical downlink control channel, PDCCH. Preferably, in this formof the invention, the predefined format has the same predetermined sizein bits as another DCI format defined in LTE.

In this case, the control signals arranged in the predefined format maybe transmitted within a common search space of the PDCCH transmission,or alternatively they may be transmitted within a search space of thedownlink transmission which is distinct from a common search space.

As already mentioned, the first and second terminals may be regarded asa group of terminals addressed by the control signal. To allow terminalsto recognise the control signal, preferably, the predefined format hasan associated cyclic redundancy code, CRC, scrambled with a group radionetwork temporary identifier, RNTI, for enabling the first and secondterminals to interpret the DCI, which is distinct from any RNTI used forother formats of DCI defined in LTE. In the specific embodiment to bedescribed, which is applied to SPS, this RNTI is called a SPS GroupC-RNTI or SPSG C-RNTI.

Various possibilities are available to reduce the amount of additionaldecoding required at the terminals. The first and second terminals maybe preconfigured to expect to receive said predefined format only inselected subframes of downlink transmission from the base station.Alternatively the method may arrange that, when a subframe contains thecontrol signal having the predefined format as defined above, no otherDCI format is employed in the same subframe. Also, in the case ofemploying the control signal to configure SPS, the novel format isoptionally only used in subframes already configured for SPS. Anotheralternative is to arrange that the UE only expects to receive a DCIformat with SPSG C-RNTI in subframes where the corresponding schedulingor reconfiguration of transmission or reception would be applicable.

In one possible form of the method, the terminals communicate with thebase station via at least one relay station, the relay station receivingcontrol signals from the base station and/or transmitting controlsignals to the terminals using said predefined format.

The method may be a machine-to-machine, M2M, or machine typecommunication, MTC, method wherein the terminals are autonomous machines(e.g., MTC devices).

Embodiments of the present invention are for use in an LTE-basedwireless communication system in which the control signals are downlinkcontrol information, DCI, and the format is a DCI format transmitted ona physical downlink control channel, PDCCH.

Here, “PDCCH” relates to any physical downlink control channel in LTE,including R-PDCCH (see above) or any control channel yet to be defined.

The one or more sets of parameters represented in the predefined formatmay be sets of parameters contained in any of the existing formatsdefined in LTE Release 8, 9, or 10 specifications. The values of one ormore bits in said predefined format may indicate one of a set ofpreconfigured PDCCH messages or partial PDCCH messages. Thus, one bit inthe predefined DCI format would allow one of two different messages tobe indicated. Two bits would allow one of four different messages to beindicated, etc.

Preferably, in this case, the predefined format provided in the presentinvention has the same predetermined size in bits as one or more of theexisting formats defined in LTE. Here, “existing formats” means formatsalready specified in the LTE standards as of the priority date,including for example formats 0, 1, 1A, 3 and 3A.

In one variant of the embodiment, the control signals arranged in thepredefined format are transmitted within a common search space of thePDCCH transmission. This has the advantage of minimising the additionaldecoding effort at the terminal.

In another variant the control signals arranged in the predefined formatare transmitted within a search space of the downlink transmission whichis distinct from a common search space. This has the advantage ofallowing a larger number of PDCH messages to be transmitted.

According to a second aspect of the present invention, there is providedbase station equipment for use in any wireless communication method asdefined above, and configured to transmit control signals in accordancewith said predefined format.

According to a third aspect of the present invention, there is provideduser equipment for use in any wireless communication method as definedabove, configured to decode control signals in accordance with thepredefined format.

Further aspects of the present invention may provide a RRM entity in awireless communication network for configuring base station equipmentand user equipment for performing any of the methods as defined above. Afurther aspect relates to software for allowing transceiver equipmentequipped with a processor to provide base station equipment or userequipment as defined above. Such software may be recorded on acomputer-readable medium.

In general, and unless there is a clear intention to the contrary,features described with respect to one aspect of the invention may beapplied equally and in any combination to any other aspect, even if sucha combination is not explicitly mentioned or described herein.

As is evident from the foregoing, the present invention involves signaltransmissions between base stations and user equipments in a wirelesscommunication system. A base station may take any form suitable fortransmitting and receiving such signals. It is envisaged that the basestations will typically take the form proposed for implementation in the3GPP LTE and 3GPP LTE-A groups of standards, and may therefore bedescribed as an eNB (eNB) (which term also embraces Home eNB or HomeeNB) as appropriate in different situations. However, subject to thefunctional requirements of the invention, some or all base stations maytake any other form suitable for transmitting and receiving signals fromuser equipments.

Similarly, in the present invention, each user equipment may take anyform suitable for transmitting and receiving signals from base stations.For example, the user equipment may take the form of a subscriberstation (SS), or a mobile station (MS), or any other suitablefixed-position or movable form. For the purpose of visualising theinvention, it may be convenient to imagine the user equipment as amobile handset (and in many instances at least some of the userequipments will comprise mobile handsets), however no limitationwhatsoever is to be implied from this. In particular the user equipmentsmay be MTC devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made, by way of example only, to the accompanying drawingsin which:

FIG. 1 schematically illustrates a basic LTE network topology;

FIG. 2 schematically illustrate a network topology for a wirelesscommunication system with MTC devices;

FIG. 3 illustrates a generic frame structure employed for the downlinkin an LTE wireless communication system;

FIG. 4 illustrates resource allocation within a frame;

FIG. 5 shows relationships between various channels defined in LTE; and

FIG. 6 is a flowchart illustrating steps in a method embodying thepresent invention.

DETAILED DESCRIPTION

Before describing embodiments of the present invention, some furtherdiscussion will be given in relation to the control channel PDCCH inLTE. However, it is to be noted that the present invention is notrestricted to application to PDCCH, or to LTE.

Following on from the discussion given in the introduction, somespecific points of relevance are as follows.

PDCCH may occupy the first 1, 2, 3 or 4 OFDM symbols in a subframe (4 isa special case for small system bandwidths). Consequently, the availablebandwidth for PDCCH is rather limited. For convenience, a PDCCH messagein accordance with a DCI format is referred to below simply as “a DCIformat”.

Existing DCI formats indicate data transmission in either DL or UL, butnot both. However, some DCI formats for DL resource scheduling may alsotrigger some kind of transmission on the UL (e.g. a SRS).

A given PDCCH may be transmitted in any one of a number of givenlocations (which is a search space comprising a pre-determined subset ofall the possible locations). The UE attempts blind decoding of the PDCCHin each location within the search space.

The UE is required to blind decode only a limited number of PDCCHcandidates. A common search space is defined for all UEs. Also,UE-specific search spaces are defined based on particular identities(RNTIs).

As already mentioned, a given PDCCH may be transmitted using identities(RNTIs) such as:

-   -   C-RNTI: UE identity for normal operation    -   SPS C-RNTI: UE identity for activating/modifying/deactivating        SPS transmission on an individual UE basis    -   TPC-PUCCH-RNTI: Group identity for Power control of PUCCH    -   TPC-PUSCH-RNTI: Group identity for Power control of PUSCH.

The RNTI is used to scramble the 16-bit CRC attached to the payload.This allows the UE to both identify whether the message has been decodedcorrectly, and confirm the RNTI value.

Each different type of message is conveyed using a different DCI format.Many PDCCH messages are intended to be received by only one UE, othersare intended for more than one UE. In particular DCI formats 3 and 3Acarry multiple power control commands, each power control commandintended for a different UE.

A specific embodiment of the present invention (see below) is applied tosemi-persistent scheduling, SPS. For SPS the following apply:

-   -   Use of SPS by a given UE may be configured independently in UL        and DL.    -   The interval between subframes with an SPS resource is        determined by RRC signalling.    -   The subset of subframes in which subsequent SPS resources occurs        is determined according to the particular subframe in which the        UE receives a PDCCH message with SPS C-RNTI. The same message        also contains details of the transmission resources etc for        PDSCH (in DL) or PUSCH (in UL).

Considering potential improvements to LTE (i.e. LTE-Advanced) to reducethe control channel overhead, possible approaches to solving the problembased on UE-specific signalling include:

(i) Reduction of the control channel message size. For DCI format sizesless than the CRC length, the CRC becomes ineffective as a mechanism forerror detection. At least one new DCI format size would be needed,potentially increasing blind decoding load. Consequently, this approachis not preferred.(ii) Control channel messages which carry multiple resource allocations.This approach has various ramifications as follows.

-   -   If the resources correspond to future subframes, this is        supported by SPS.    -   If the resources correspond to different carriers, for small        packets it would be more efficient to use only one carrier. That        is, when using multiple carrier frequencies (so-called carrier        aggregation), sending a small packet on each carrier would        currently require transmission of one DCI format (or PDCCH        message) per carrier. Therefore, in terms of control channel        overhead, it would be more efficient to combine the several        small packets into one larger packet, and send this on one        carrier. This would require transmission of just one DCI format        in total.    -   UL and DL resource allocations can be carried in the same        message.

Following approach (ii), an embodiment of the present invention, asapplied to LTE, involves transmitting multiple UE-specific resourceallocations in a single DCI format containing information for multipleUEs. It is noted that for many applications the same set of parametervalues or selection from a small set of different parameter values issufficient, and this fact can be exploited to save bits.

The selection between sets of parameter values is indicated by one ormore individual bits. Thus, in the present embodiment, sets of one ormore bits, each set intended for a different UE, are transmitted in onePDCCH message, using a new DCI format. The sets of parameter values may,for example, be determined by higher layer (e.g. RRC) signalling,dynamically (e.g. via PDCCH) or fixed in the system specification.

The new DCI format could be distinguished from an existing DCI format,by having a different size (number of payload bits). However, in orderto avoid increasing the number of blind decodes, the size of the new DCIformat is the same as that of an existing DCI format. Preferably thesize is the same as DCI formats 0/1A/3/3A, and is transmitted either inthe common search space, or in another search space. For convenience,the new format is referred to below as “3B”, though it will beunderstood that the particular label given is unimportant.

In terms of the LTE specification 3GPP 36.212, embodiments of thepresent invention involve the definition of a new DCI format, as in thefollowing:—

Format 3B DCI format 3B is used for the transmission of DCI bits. Thefollowing information is transmitted by means of the DCI format 3B:  -DCI bit number 1, DCI bit number 2, ..., DCI bit number M where M =L_(format 0), and where L format0 is equal to the payload size of format0 before CRC attachment, including any padding bits appended to format0. Parameters provided by higher layers determine the indices to the DCIbits, and the interpretation of those bits for a given UE.

However, it is advantageous to be able to distinguish the new DCIformat, which could be done using a specific identity (RNTI). In termsof the LTE specification 36.213, embodiments of the present inventionmake use of a new RNTI such as the following:—If a UE is configured byhigher layers to decode PDCCHs with the CRC scrambled by theDCI-BIT-RNTI, the UE shall decode the PDCCH according to the combinationdefined in table 8.9.

TABLE 8-9 PDCCH configured by DCI-BIT-RNTI DCI format Search Space DCIformat 3B Common

Each possible value of a group of one of more DCI bits can indicateparameters equivalent to one of a set of preconfigured PDCCH messages(or partial PDCCH messages).

Additional parameters could be included, such as indication of a timingoffset between the subframe in which the new DCI is received and thesubframe in which the indicated parameters are to be applied.

A given DCI bit may used to signal to a single UE, or a group of UEs.

There are several advantages of this scheme. It allows the possibilityof very low PDCCH overhead. There is almost no increase in blinddecoding complexity if the new DCI format is the same size as DCIformats 0/1A, since this requires only an additional CRC check. There isthe possibility of improved reliability compared with a UE specific DCIformat (for many UEs), since the common PDCCH message can be transmittedwith more energy without a significant cost in overhead. Additionally,there is the possibility of combining the functionality of both DCIformats 3 and 3A for both PUSCH and PUCCH power control.

The new scheme can provide similar features to SPS as currently definedin LTE but with more flexibility, allowing better support for variablepacket sizes and variable intervals between packets. A specific use forthe new scheme is to support retransmissions using SPS in the UL, wherecurrently a first transmission requires no PDCCH, but a retransmissionrequires a full PDCCH.

The scheme as outlined above has less signalling flexibility comparedwith the existing DCI formats. However, if more flexibility is needed ina particular subframe, then one of the existing formats can be usedinstead, as is currently supported in LTE. As noted, there would be thevery small additional computation of an additional CRC check.

First Embodiment

In a first embodiment based on LTE, the network operates using FDD andcomprises one or more eNBs, each controlling at least one downlink cell,each downlink cell having a corresponding uplink cell. Each DL cell mayserve one or more terminals (UEs) which may receive and decode signalstransmitted in that cell. In order to schedule the appropriate use oftransmission resources in time, frequency and spatial domains fortransmission to and from the UEs, the eNBs send control channel messages(PDCCH) to the UEs.

As already mentioned, a PDCCH message typically indicates whether thedata transmission will be in the uplink (using PUSCH) or downlink (usingPDSCH), it also indicates the transmission resources, and otherinformation such as transmission mode and data rate. The UE performsblind decoding for a number of possible PDCCH message types (DCIformats) over a defined search space on the downlink primary cell(Pcell). A given UE is configured by higher layer signalling (e.g. RRCsignalling) to receive a DCI format (e.g. DCI format 3B) in the commonsearch space. The CRC of DCI Format 3B is scrambled by an RNTI (e.g.DCI-BIT-RNTI). Parameters provided by higher layers (e.g. RRC) determinethe indices to the DCI bits for the given UE, and the interpretation ofthose bits for the given UE.

In a preferred version of this first embodiment, the values of at leastone of the DCI bits indicates a selection from a set of preconfiguredDCI messages. Each member of the set of preconfigured DCI messagescorresponds to set of values for each parameter of interest. As anexample the set of parameters could correspond to those which could betransmitted using an existing DCI format. One DCI bit in the new format3B would allow one of two different messages to be indicated. Two DCIbits would allow one of four different messages to be indicated, etc.

This would be suitable for applications where limited flexibility (e.g.in resource allocation, or data rate) is acceptable (e.g. where the sameresource allocation is used frequently) in return for very low controlchannel overhead, such as for MTC or VoIP. SPS achieves this but is evenless flexible, particularly in terms of fixed data rates and timing ofresource allocation. For subframes where the restriction of using apreconfigured set of parameters in not acceptable, then an existing DCIformat can be used instead.

FIG. 6 is a flowchart for illustrating steps in a method forconstructing DCI in this case. Thus, the method begins (step S10) withan eNB (or higher level node, or suitably-capable RN) scheduling anallocation of resource for a UE either on DL or UL, producing somescheduling information (denoted DCI in the Figure for simplicity). Thenit is checked (S20) whether the newly-generated scheduling informationfits a preconfigured message, or in other words whether the parametervalues it contains coincide with a predetermined set of parametervalues. If so, it is suitable for use with the new format in accordancewith the present invention and the PDCCH is accordingly constructedusing the new format “3B” in step S30. This PDCCH message may bespecific to a single terminal, or may be common to a group of terminals.The scheduling information may be for SPS (see below). If the schedulinginformation does not fit a preconfigured message, it is necessary toconstruct a specific PDCCH message for that terminal using one of theexisting DCI formats in step S40. In either case, the next step (S50) isto check whether there are any more terminals which the eNB needs toschedule in the subframe being scheduled. If so then the process returnsto the beginning; however, if not (in other words all terminals havebeen scheduled), the resultant PDCCH messages (for example, one or moremessages in each of old and new DCI formats) is transmitted in step S60.The process will normally repeated for every subframe, assuming that atleast some UEs require dynamic scheduling which is subject to change ona per-subframe basis. However, it is to be noted that the schedulinginformation need not apply to the next subframe. As mentioned below, onepossible parameter is a time delay (e.g., number of subframes) beforeother scheduling information takes effect. Such a time delay may also bedetermined implicitly, for example a different delay value may beconfigured for each of several terminals.

As an example, for FDD at least one of the preconfigured messagesindicated by format 3B contains values for the following UL grant, whichwould otherwise be sent using DCI format 0:—

-   -   Frequency hopping flag    -   Resource block assignment and hopping resource allocation    -   Modulation and coding scheme and redundancy version    -   New data indicator    -   TPC command for scheduled PUSCH    -   Cyclic shift for DM RS and OCC index    -   CSI request    -   SRS request    -   Multi-cluster flag

In the above list, DM RS is the above-mentioned demodulation referencesignal. The cyclic shift and OCC (orthogonal cover code) indexcharacterise the DM RS. SRS refers to a Sounding Reference Signal usedby the eNB to estimate the quality of the uplink channel. Themulti-cluster flag is used to indicate non-contiguous (called“multi-cluster”) resource allocation on the uplink. Other parameters areas mentioned previously.

Note that it will not be necessary in every case to indicate all thevalues corresponding to a DCI format. For example, TPC commands may notbe required. Default values may be defined for values not included.

As a further example, for FDD at least one of the preconfigured messagesindicated by format 3B contains values for the following DL assignment,which would otherwise be sent using DCI format 1A:—

-   -   Localized/Distributed VRB assignment flag    -   Resource block assignment    -   Modulation and coding scheme    -   HARQ process number    -   New data indicator    -   Redundancy version    -   TPC command for PUCCH    -   SRS request

Here, the VRB assignment flag is used to indicate whether VirtualResource Blocks assigned to a UE are contiguous (“Localized”) ornon-contiguous (“Distributed”). Redundancy version relates to HARQ andallows retransmission of a codeword multiple times until it issuccessfully received. The other parameters are as outlined already.

Note that additional information may be included, for example indicationof resources to be used for PUCCH. Information not normally part of aDCI format may also be included e.g. ACK/NACK for data sent on PUSCH,time delay between reception of DCI format and validity of UL or DLassignment.

In a variation of this embodiment, DCI format 3B may simultaneouslycarry bits corresponding to more than one set of DCI e.g. both UL and DLassignments.

In a further variation of this embodiment, the set of preconfiguredmessages may include sets of values broadly corresponding to more thanone DCI format. This can allow an indication of a selection of one set(or more, in the case of both UL and DL) from a plurality of sets ofpreconfigured parameters. As well as containing different values,different sets of parameters could correspond to contents of differentDCI formats (not restricted to 0 and 1A).

In a further variation of this embodiment groups of one or more DCI bitsin format 3B may simultaneously carry one or more of the following, e.g.according to RRC configuration:—

-   -   DL assignment on PDSCH    -   UL assignment on PUSCH    -   1 bit TPC commands for PUCCH    -   2 bit TPC commands for PUCCH    -   1 bit TPC commands for PUSCH    -   2 bit TPC commands for PUSCH    -   ACK/NACK for a codeword sent on PUSCH    -   ACK/NACK for a code block within a codeword sent on PUSCH    -   SRS trigger    -   CSI report trigger    -   Activation/deactivation of SPS    -   Activation/deactivation of DRX/DTX    -   Activation/deactivation of carriers    -   Status of DL data buffer at the eNB    -   Indication of message type (i.e. contents of the parameter set);    -   Indication to ignore message contents or otherwise; and    -   Time delay before a parameter is applied.

Here, the item “Indication of message type” is used to allow the sameset of bits to indicate different parameters. The “Indication to ignoremessage contents or otherwise” can be used in case there is no messageor parameter value intended for the terminal expecting to decode thecorresponding bits, in other words a “no action” flag.

As a further variation the new format 3B could be transmitted in anadditional or alternative search space (e.g. a UE-specific searchspace).

Second Embodiment

A second embodiment is similar to the first embodiment except that agiven DCI bit is used to convey information to more than one UEsimultaneously. The interpretation of the information bit may be thesame or different for different UEs, for example corresponding todifferent RRC configurations of UL and/or DL assignments. A group of UEsis defined by configuring them with the same value of DCI-BIT-RNTI.

In a preferred version of this second embodiment, format 3B is used toconvey the same command to a number of UEs. For example:—

-   -   Change of state (e.g. to idle mode or “off” state)    -   Request to transmit data (e.g. one or more sensor measurements        or meter readings)    -   Change in application level data (e.g. change in electricity        tariff, in the case of an electricity meter).

In this instance, an additional/alternative (or possibly extended)search space would be more appropriate. The advantage is that a largersearch space makes it possible to transmit more PDCCH messages.Currently in LTE the common search space (for broadcasting PDCCHmessages to multiple UEs) is rather restricted.

The acknowledgement of successful reception of such a command could becarried using preconfigured resources (e.g. on PUCCH or using PUSCHaccording to a previously configured UL grant). In order to avoid allUEs responding at the same time, different UEs would be configured torespond after different amounts of time delay.

Specific Embodiment SPS

As a specific embodiment of the present invention, we now considerpotential improvement to SPS operation in LTE (i.e. LTE-Advanced) toimprove operational flexibility but with low control channel overhead.

The specific embodiment is intended to be applied to SPS, so that theindicated set of parameter values for a given UE is applied to theoperation of SPS for that UE. For example this can be achieved bymodification of the parameters applying to a single transmissionscheduled according to SPS, or modification of the parameters to beapplied subsequently.

In this case, the new Format 3B already outlined above is modified asfollows: If a UE is configured by higher layers to decode PDCCHs withthe CRC scrambled by the SPSG C-RNTI, the UE shall decode the PDCCHaccording to the combination defined in table 8.9.

TABLE 8-9 PDCCH configured by SPSG C--RNTI DCI format Search Space DCIformat 3B Common

The SPSG C-RNTI is a new RNTI indicating a group of UEs configured forSPS operation. It is to be distinguished from SPS C-RNTI already definedin LTE for a single UE.

Use of this scheme for SPS allows much greater operational flexibilityfor SPS, compared with conventional SPS where a specific PDCCH messageis required to modify the SPS configuration. The term “SPS” is thereforeto be interpreted broadly as encompassing more flexible semi-persistentscheduling schemes in addition to the conventional SPS defined in LTE.

Whilst operational flexibility is improved in this embodiment, thesignalling flexibility is reduced compared with use of the existing DCIformat to modify SPS transmissions, since the UEs are addressed as agroup. However if more flexibility is needed in a particular subframe,then one of existing formats can be used instead, as is currentlysupported in LTE. As noted previously, if the new DCI format is the samesize as one of the existing formats, there is only the very smalladditional computation of an additional CRC check to test for thepresence of SPSG C-RNTI.

The conventional SPS C-RNTI can continue to be used. That is, the UE maybe configured to receive DCI formats with CRC scrambled by SPS C-RNTI,which may activate, modify or deactivate SPS operation on an individualUE basis. In the case of SPS, the period between SPS transmissions isconfigured by RRC signalling independently for UL and DL.

In a first form of this embodiment, a UE which is configured for SPSoperation (and receive DCI formats with CRC scrambled by SPS C-RNTI) mayalso be configured to receive a new DCI format with CRC scrambled bySPSG C-RNTI. Assuming that SPS operation is activated (e.g. by receptionof an appropriate PDCCH message), the value of a particular (first)information bit in the new DCI format indicates whether or not the UEshould expect a PDSCH transmission in the DL (according to predeterminedSPS parameters) in the same subframe. The predetermined SPS parametersmay be signalled by RRC or in a PDCCH message. Similarly, a different(second) information bit may indicate whether the UE should transmitPUSCH in the UL. The particular information bits carrying theseindications is predetermined (e.g. configured by RRC signalling). Thatis, each UE knows where in the format to find the (or each) set of bitsintended for that UE.

In other words, the first form allows a PDCCH message to be constructedwhich addresses a group of UEs, but which causes SPS to be activated ordeactivated on a per-subframe basis for each terminal separately, andindependently for UL and DL.

In a variation of the first form, the reception of a DCI format withSPSG C-RNTI in a particular subframe modifies SPS operation so that theperiodic transmission and/or reception according to the SPS parameterscontinue from that subframe. In other words, reception of the DCI formatoverrides any existing parameter values set up for SPS with valuescontained in the DCO format (either explicitly or signified as aselection among sets of predetermined values).

In a second form, which is otherwise like the first form of the SPSembodiment, when the UE receives a DCI format with SPSG C-RNTI, thevalues of a further set of information bits indicates the subframe inwhich SPS transmission and/or reception should take place. This could beby means of the information bits indicating an offset relative to thesubframe in which the DCI format is received. Different UEs may beconfigured with different offsets or sets of offsets.

In a third form, which is otherwise like the first form, when the UEreceives a DCI format with SPSG C-RNTI, the value of a particularinformation bit activates/deactivates SPS operation. Again, this may bedone in common for the group of UEs, or individually for each UE in thegroup addressed by the SPSG C-RNTI.

In a fourth form, which is otherwise like the first form, when the UEreceives a DCI format with SPSG C-RNTI, the values of a particular setof information bit indicates a selection from one among a pre-determinedset of SPS transmission and/or reception parameter values which are tobe used by the UE. The pre-determined set of SPS parameters may besignalled by RRC. Thus, unlike the first form which essentially onlyactivates/deactivates SPS, this form of the embodiment additionallyconfigures values of a set of parameters for SPS.

In a fifth form of the SPS embodiment, which is otherwise like the firstform, when the UE receives a DCI format with SPSG C-RNTI, the values ofa particular set of information bits indicates one of a pre-determinedset of carrier frequencies which are to be used for SPS transmissionand/or reception by the UE. Once again this indication may either be onan individual terminal basis, or for the group collectively.

Various techniques may be used in this embodiment to limit the amount ofblind decoding required at the UE side.

In a sixth form, which is otherwise like the first form, each UE in thegroup is configured to expect to receive a DCI format with SPSG C-RNTIonly within a subset of the available subframes. For example,transmission of DCI format with SPSG C-RNTI may be restricted tosubframes corresponding to a period and an offset, which may beconfigured by RRC signalling. This restriction may limit the number ofadditional blind decodes. In addition a higher number of active UEs canbe supported.

As a variation, in subframes where the UE expects to receive a DCIformat with SPSG C-RNTI, it does not also expect to receive a DCI formathaving a different size with C-RNTI. As a further variation, the UE onlyexpects to receive a DCI format with SPSG C-RNTI in subframes configuredfor SPS transmission and/or reception.

In seventh form, which is otherwise like the first form, the UE onlyexpects to receive a DCI format with SPSG C-RNTI, in subframes with apre-determined delay following an SPS transmission in the UL. Thissupports the scheduling of retransmissions.

The above forms of the specific embodiment may also be modified totransmit other information, such as power control commands, using thenew DCI format. In other words, the specific embodiment, whilstprimarily intended to configure SPS-type operation at terminals, may beused to convey additional control information not necessarily related toSPS.

As an example, SPS parameters for which parameter values may be definedin the above-mentioned set of SPS transmission and reception parameters(for example in the fourth form already mentioned) could include:

-   -   Frequency hopping flag    -   Resource block assignment and hopping resource allocation    -   Modulation and coding scheme and redundancy version    -   Cyclic shift for DM RS and OCC index    -   TPC (transmit power control) commands    -   CSI request    -   SRS request    -   Multi-cluster flag

Relay Embodiment

A further embodiment is similar to the above embodiments, but thecontrol channel transmission is from an eNB to a relay node (RN). Thisuses R-PDCCH as mentioned above and described in 3GPP TS36.216, insteadof PDCCH, for the DL control channel. The features of the first and/orsecond embodiments may be applied.

Of particular interest would be the possibility of using DCI format 3Bto transmit ACK/NACK from the eNB to one or more RNs for datatransmitted in the uplink from RNs to eNB using PUSCH, since suchACK/NACK transmission is not currently supported. Normally, for ULtransmissions on PUSCH from UE to eNB the ACK/NACK indicating correctreception of PUSCH (or otherwise) is carried by the PHICH. If the UEreceives a NACK it would perform a retransmission using the sameresources as the first transmission (without needing a grant on PDCCH).Alternatively, different retransmission resources can be grantedexplicitly using PDCCH. However, use of PHICH is not defined for usewith PUSCH transmitted from RN to eNB (and it would not be easy to doso). In this case NACK would be implied if PDCCH indicates resources fora retransmission (otherwise ACK is assumed). So PDCCH is always sent.However, it could be advantageous (in reducing control channel overhead)to support explicit ACK/NACK.

Note that most scenarios considered in 3GPP discussions assume thatthere would be only a few relay nodes per donor cell. However, futurescenarios could include large number of devices per cell using theR-PDCCH e.g. for MTC.

Thus, to summarise, an embodiment of the present invention may provide ascheme for transmission of control channel information in a compactform. The main advantages are as follows:—

-   -   Possibility of very low PDCCH overhead, suitable for efficient        transmission of very low data payloads.    -   Almost no increase in blind decoding complexity if the new DCI        format is the same size as DCI formats 0/1A, since this would        require only an additional CRC check.    -   Possibility of improved reliability than UE specific DCI format        (for many UEs), since the common PDCCH message can be        transmitted with more energy without a significant cost in        overhead. That is, PDCCH messages can be made more reliable by        adding additional redundancy (which may be by repetition of        bits). In LTE the total message size can then be increased by a        factor of 2, 4 or 8. This factor is referred to as the        aggregation level.    -   Possibility of combining the functionality of both DCI formats 3        and 3A for both PUSCH and PUCCH power control within a single        instance of PDCCH transmission.    -   Better support for variable packet sizes and variable intervals        between packets than currently defined SPS.

A specific use for the invention is for SPS, including to supportretransmissions using SPS in the UL, where currently a firsttransmission requires no PDCCH, but a retransmission requires a fullPDCCH. Currently, for the special case of SPS (Semi-PersistentScheduling), transmission of NACK (on PHICH) to request a retransmissionby the UE is not supported. A retransmission in the UL requires anexplicit resource grant.

Various modifications are possible within the scope of the presentinvention.

The new format described with respect to an embodiment of the presentinvention was referred to as “3B” for convenience, but the designationused is not essential. More than one distinct format may be definedusing the principle of the present invention. However, it is preferablefor any new format defined in accordance with the present invention tohave the same size (in bits) as formats already defined in LTE, so as toreduce the additional blind decoding otherwise required.

The new format has been described in relation to PDCCH, but it is to beunderstood that this includes R-PDCCH as well as any other physical DLcontrol channels whether or not denoted by PDCCH.

Any of the embodiments and variations mentioned above may be combined inthe same system. Whilst the above description has been made with respectto LTE and LTE-A, the present invention may have application to otherkinds of wireless communication system also. Accordingly, references inthe claims to “user equipment” are intended to cover any kind ofsubscriber station, MTC device and the like and are not restricted tothe UE of LTE.

Although the new format(s) in accordance with the present invention canbe applied to more than one UE simultaneously, this is not essential.The new format may advantageously be applied even to a single UE wherethe use of preconfigured messages allows more information to be conveyedwithin the available number of bits. Thus, for example, both UL and DLallocations for the same UE may be indicated within the same PDCCHmessage.

In this case, it may be preferable to employ the UE-specific searchspace (as for other DCI formats intended for a single UE), rather thanthe common search space.

The third embodiment relating to R-PDCCH may find application in futureto transmission from eNB to UEs (i.e. without involvement of RNs), sincesuch a use of R-PDCCH is under discussion.

In any of the aspects or embodiments of the invention described above,the various features may be implemented in hardware, or as softwaremodules running on one or more processors. Features of one aspect may beapplied to any of the other aspects.

The invention also provides a computer program or a computer programproduct for carrying out any of the methods described herein, and acomputer readable medium having stored thereon a program for carryingout any of the methods described herein.

A computer program embodying the invention may be stored on acomputer-readable medium, or it may, for example, be in the form of asignal such as a downloadable data signal provided from an Internetwebsite, or it may be in any other form.

It is to be understood that various changes and/or modifications may bemade to the particular embodiments just described without departing fromthe scope of the claims.

To summarise, embodiments of the present invention provide a scheme fortransmission of control channel information in a compact form. Aspecific embodiment is intended to support SPS (Semi-PersistentScheduling). As applied to LTE, the main feature is to indicate apre-configured UE-specific resource allocation in a Downlink ControlInformation (DCI) format containing information for multiple UEs in thesame PDCCH.

In other words, by means of the present invention, the same PDCCH may beused to address a group of terminals, but different parts of the DCIformat may be intended for different terminals within the group. Thisdoes not exclude one part (set of bits) being used to send a commoncontrol message to all terminals in the group.

In order to avoid increasing the number of blind decodes, the DCI formatsize may be the same as an existing DCI format. Preferably, the size isthe same as DCI formats 0/1A/3/3A, and is transmitted in the commonsearch apace. The number of required bits per UE is minimised bysignalling only one of a limited set of DCI messages per UE.

Applied to SPS, the main advantages are as follows:—

-   -   Better support for variable packet sizes and variable intervals        between packets than currently defined SPS    -   Possibility of very low PDCCH overhead, suitable for efficient        transmission of very low data payloads (eg: for Machine to        Machine communication and sensor communication traffic).    -   Almost no increase in blind decoding complexity if the new DCI        format is the same size as DCI formats 0/1A, since this would        require only an additional CRC check.    -   Possibility of improved reliability than UE specific DCI format        (for many UEs), since the common PDCCH message can be        transmitted with more energy without a significant cost in        overhead.

In particular the present invention can be used to improve supportretransmissions using SPS in the UL, where currently a firsttransmission requires no PDCCH, but a retransmission requires a fullPDCCH.

INDUSTRIAL APPLICABILITY

Embodiments of the present invention allow transmission of UE-specificresource allocations in a Downlink Control Information (DCI) formatcontaining information for multiple UEs in the same PDCCH. Currently inLTE, a single control channel (PDCCH) is transmitted to the UE for anyUL or DL resource allocation, except for semi-persistent scheduling(SPS). The invention modifies the control channel operation, providingan additional means, in particular a new combinatory set ofpreconfigured messages, for efficiently transmitting control informationfor those instances where full flexibility is not required. In order toavoid increasing the number of blind decodes, the size of the new DCIformat (3B) is the same as an existing DCI format, preferably same asthe size of DCI formats 0/1A/3/3A, and is transmitted in the commonsearch space. The number of required bits is reduced by signalling onlyone of a limited set of DCI messages per UE. Thus the PDCCH iseffectively able to support an increased number of UEs.

1. A wireless communication method in which a base station transmits acontrol signal, the control signal arranged in accordance with apredefined format having a predetermined size in bits and comprising oneor more sets of bits each containing one or more bits; wherein a firstset of bits within the format is intended for a first terminal and a setof bits within the format is intended for a second terminal; and whereinthe timing of subsequent transmission and/or reception by the firstterminal is determined by the control signal.
 2. The wirelesscommunication method according to claim 1 wherein the timing ofsubsequent transmission and/or reception by the first terminal dependson the timing of reception of the control signal.
 3. The wirelesscommunication method according to claim 1 wherein the timing ofsubsequent transmission and/or reception by the first terminal dependson the value(s) of the first set of bits.
 4. The wireless communicationmethod according to claim 1 wherein a second set of bits in the controlsignal, distinct from the first set of bits, is intended for the secondterminal.
 5. The wireless communication method according to claim 1,wherein the first set of bits is also intended for the second terminal.6. The wireless communication method according to claim 1, wherein thesets of bits include sets of bits representing values of one or moreparameters.
 7. The wireless communication method according to claim 4wherein the first and second sets of bits represent the sameparameter(s).
 8. The wireless communication method according to claim 1wherein the sets of bits include sets of bits representing a selectionamong predetermined sets of parameter values.
 9. The wirelesscommunication method according to claim 6 wherein the parameter values,or the predetermined sets of parameter values, include parameter valuesfor scheduling transmission and/or reception of the first and secondterminals.
 10. The wireless communication method according to claim 1wherein transmission and/or reception by the first terminal occurs inunits of subframes and the first set of bits includes at least one bitindicating any one of: whether transmission and/or reception is to beperformed in the current subframe either on a downlink and/or on anuplink; whether transmission and/or reception is to be performed insubsequent subframes either on a downlink and/or on an uplink; whethertransmission and/or reception is to be performed in a defined subframewhich is a defined number of subframes from the current subframe;whether semi-persistent scheduling, SPS operation is to be activated ordeactivated; a selection among predetermined sets of parameter valuesfor scheduling; and a selection among a predetermined set of carrierfrequencies for scheduling.
 11. The wireless communication methodaccording to claim 1 for use in an LTE-based wireless communicationsystem in which the control signals are downlink control information,DCI, and said predefined format is a DCI format transmitted on aphysical downlink control channel, PDCCH.
 12. The wireless communicationmethod according to claim 11, wherein the predefined format has the samepredetermined size in bits as another DCI format defined in LTE.
 13. Thewireless communication method according to claim 11 wherein the controlsignals arranged in the predefined format are transmitted within acommon search space of the PDCCH transmission.
 14. The wirelesscommunication method according to claim 11 wherein the control signalsarranged in the predefined format are transmitted within a search spaceof the downlink transmission which is distinct from a common searchspace.
 15. The wireless communication method according to claim 11wherein the predefined format has an associated cyclic redundancy code,CRC, scrambled with a group radio network temporary identifier, RNTI,for enabling the first and second terminals to interpret the DCI, whichis distinct from any RNTI used for other formats of DCI defined in LTE.16. The wireless communication method according to claim 1 wherein thefirst and second terminals are preconfigured to expect to receive saidpredefined format only in selected subframes of downlink transmissionfrom the base station.
 17. Base station for use in a wirelesscommunication system comprising: the base station, a first terminal anda second terminal; the base station configured to transmit a controlsignal, the control signal arranged in accordance with a predefinedformat having a predetermined size in bits and comprising one or moresets of bits each containing one or more bits; wherein a first set ofbits within the format is intended for the first terminal and a set ofbits within the format is intended for the second terminal; and whereinthe timing of subsequent transmission and/or reception by the firstterminal is determined by the control signal.
 18. Terminal for use in awireless communication system comprising the terminal, a secondterminal, and a base station, the terminal configured to receive fromthe base station and decode a control signal, the control signalarranged in accordance with a predefined format having a predeterminedsize in bits and comprising one or more sets of bits each containing oneor more bits; wherein a first set of bits within the format is intendedfor the terminal and a set of bits within the format is intended for thesecond terminal; and wherein the timing of subsequent transmissionand/or reception by the terminal is determined by the control signal.19. One or more non-transitive computer-readable recording media onwhich are stored computer-readable instructions which, when executed bya processor of a transceiver device in a wireless communication system,cause the device to provide the base station according to claim
 17. 20.A wireless communication system comprising: a base station, a firstterminal and a second terminal; the base station configured to transmita control signal, the control signal arranged in accordance with apredefined format having a predetermined size in bits and comprising oneor more sets of bits each containing one or more bits; wherein a firstset of bits within the format is intended for the first terminal and aset of bits within the format is intended for the second terminal; andwherein the timing of subsequent transmission and/or reception by thefirst terminal is determined by the control signal.